Chronic lameness can be a frustrating problem for owners of equine athletes. When nerve blocks, radiographs (X rays), and ultrasounds yield no definitive answers, where can a veterinarian turn next? According to recent study results, magnetic resonance imaging (MRI) appears to be a beneficial next step for diagnosing some leg lamenesses when a veterinarian cannot provide a definitive diagnosis for the lameness using conventional techniques.

"An accurate diagnosis enables the veterinarian to estimate prognosis and to advise on appropriate treatment and management," said Annamaria Nagy, DVM, MRCVS, of the Center for Equine Studies at the Animal Health Trust in Newmarket, Suffolk, U.K.

An MRI produces three-dimensional images of bone and soft tissue, while radiographs produce two-dimensional images that detect bone problems. Alternatively, ultrasonography can visualize muscles, tendons, and many internal organs to capture their size, structure, and any lesions.

To determine if MRI examinations are beneficial for use in diagnosing lameness localized to the carpus and/or proximal metacarpal region, Nagy et al. reviewed the records of 72 MRI scans on 58 limbs in 50 horses, ranging in age from 2 to 17 years. The horses included in the study represented a variety of breeds and were used for a variety of activities. The duration of lameness ranged from one week to two years.

The horses were presented for lameness examination at the Animal Health Trust between January 2003 and September 2010. Cases were selected for review if "lameness was localized to the carpus of metacarpal region using (nerve blocks), but the results of radiographic and ultrasonographic examinations were equivocal or not consistent with the degree of lameness" the horse displayed.

Upon reviewing the results, the team found that the MRI picked up different ailments and a wider range of abnormalities in the lame horses than did radiographs or ultrasounds, which allowed veterinarians to make a better and more accurate diagnosis.

While MRIs are more costly than other diagnostic options, Nagy said, she would--as an owner--consider having an MRI performed on a lame horse when the results of the clinical examination, nerve and joint blocks, and traditional diagnostic imaging modalities do not explain the lameness.

"It is important to recognize that MRI may not give the final answer, either," she cautioned. "Occasionally other imaging techniques, such as scintigraphy (bone scan), are needed. In some horses no diagnostic quality images can be obtained either due to the horse's temperament or due to slight movement--some horses sway when sedated, which results in poor image quality and sometimes in inability to acquire images."

The study, "Magnetic resonance imaging findings in the carpus and proximal metacarpal region of 50 lame horses," will be published in an upcoming edition of the Equine Veterinary Journal. The abstract is available online.

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